Priority to German Patent Application No. 10139577.9, filed Aug. 10, 2001 and hereby incorporated by reference herein, is claimed.
The present invention relates to an electrical device including at least one flexible conductor and to a method for manufacturing such an electrical device.
Flexible conductors, which are used, in particular, as electrical current conductors or data conductors, are employed for different applications. Apart from so-called xe2x80x9cbare conductorsxe2x80x9d, which do not feature an outer insulation layer, usual conductors are, in particular, conductors having an insulating layer. Regardless of this, the conductor can be provided on the outer surface with a flexible or a rigid layer, for example, a plastic sheathing, which serves, in particular, as a protection against mechanical stress.
German Patent Document No. 196 09 253 describes a method for injection molding of plastic parts featuring an electrical conductor which is molded around in the insulating plastic part and can be designed, for example, to be flexible. The electrical conductor features an electrical contact point only at the ends. In this method, a bare conductor is inserted into the mold cavity of an open mold with a certain part of its length and there mechanically pre-fixed prior to the start of the injection process. In this design approach, moreover, additional fixing points, so-called xe2x80x9cchanging fixing pointsxe2x80x9d, are used. This design approach is only suitable for electrical conductors which must be guaranteed to be completely embedded. The electrical conductor features an electrical contact only at its ends.
The design approach identified in German Patent Document No. 196 09 253 fails in application cases where only a partial embedding is required, in particular, where a locally defined omission of the embedding is required.
An object of the present invention is to provide an electrical device which has at least one flexible conductor featuring an electrically insulating embedding and an arbitrary number of electrical contact areas as well as to provide an inexpensive method for manufacturing such a device.
This objective may be achieved in that the embedding is removed from the contact areas on the side of the wall facing the surface and in that the contact areas bound the surface of the wall.
Along the lines of the present invention, contact areas are usual contact points located between electrical current and/or data conductors and secondary electrical components or elements, such as a semiconductor component, a sensor, a transducer, a switch or a device connector, in particular, for the purpose of electrical current and/or data transmission.
In this context, the physical connection of these parts is accomplished in a usual manner so that, in particular, an electrical current and/or data transmission is ensured between these parts.
An advantageous embodiment of the present invention is geared to providing at least one contact area which projects above the surface level of the adjacent wall. This arrangement of the contact area allows the device according to the present invention to be manufactured in a particularly economical manner since the flexible conductor is pressed into a recess in the interior space of the mold prior to introducing the plastic, which minimizes the effort for fixing in position the flexible conductor subsequently.
The aforementioned arrangement is particularly expedient if the device according to the present invention is an electrical device in which a plurality of contact areas are regularly arranged on the outer surface of the housing such as the contact areas for the keypad of a telephone.
Moreover, it is preferred for the wall to have a rigid and dimensionally stable design. This design ensures high mechanical load capability of the device.
The plastic which is preferably used as the base material for the embedding within the scope of the present invention has regularly electrically insulating properties. A plastic which features this property secondarily or not at all is claimed alternatively. Moreover, a plastic is preferred which is machinable after the injection process, a foamed plastic being, in principle, also usable within the scope of the present invention.
Moreover, the object of the present invention may be achieved by a method for manufacturing an electrical device according to the present invention, in which a flexible conductor is inserted into the mold cavity of an open mold and mechanically fixed in position prior to the start of the injection process and, upon closure, the remaining free space of the mold cavity is filled with liquid plastic after which the plastic solidifies, the mold cavity is opened and the device is removed, the conductor being pressed together with the inner wall of the mold cavity in a sealing and immovable manner only in the region of contact areas and, at the remaining locations, being held at a distance from the inner wall.
To achieve the object according to the present invention the flexible conductor should be pressed against the inner wall of the mold at the intended locations of the corresponding contact areas in as sharply contoured and impervious a manner as possible with regard to ingress of liquid plastic and/or other media during injection molding or of foamable plastic and/or other media during foaming. In this context, according to the present invention, the mechanical pre-fixing is designed such that the above described pressing takes place at least until the plastic has solidified in a dimensionally stable manner. The positioning, i.e., in particular, the holding of the flexible conductor in the desired position and/or the secure fixing in this position can be accomplished through means in a permanent, temporary or alternating manner at least while the plastic is introduced into the remaining interior space of the mold in a manner known per se.
It is preferred for at least a part of the pressing means to be mechanical pressing means. Further pressing means along the lines of the present invention are hydraulic means such as hydraulic pressure cylinders but also injection nozzles or injection nozzle systems for introducing the liquid plastic and/or other media as, for example, compressed air into the interior space of the mold. It is particularly expedient to use the mass and/or media flow introduced via the nozzles as a means along the lines described above.
Further pressing means according to the present invention are physical fields such as magnetic fields which, at least temporarily, cause or assist the flexible conductor to be pressed against the inner side of the mold. Alternatively, the desired pressing can be accomplished by temporarily applying negative pressure. The above enumeration of means is not to be regarded as conclusive.